Fix null URL handling in "get noopener for window open"

Closes #10844. Also handles the case of a blob: URL with a null blob URL entry, e.g., window.open('blob:https://video_url').

Author: domenic

source

@@ -89901,12 +89901,13 @@ dictionary <dfn dictionary>WindowPostMessageOptions</dfn> : <span>StructuredSeri
 
   <p>To <dfn>get noopener for window open</dfn>, given a <code>Document</code>
   <var>sourceDocument</var>, an <span>ordered map</span> <var>tokenizedFeatures</var>, and a
-  <span>URL record</span> <var>url</var>, perform the following steps. They return a boolean.</p>
+  <span>URL record</span>-or-null <var>url</var>, perform the following steps. They return a
+  boolean.</p>
 
   <ol>
    <li>
-    <p>If <var>url</var>'s <span data-x="concept-url-scheme">scheme</span> is "<code
-    data-x="">blob</code>":</p>
+    <p>If <var>url</var> is not null and <var>url</var>'s <span
+    data-x="concept-url-blob-entry">blob URL entry</span> is not null:</p>
 
     <ol>
      <li><p>Let <var>blobOrigin</var> be <var>url</var>'s <span